Hydraulic servomotor



April ,1 E. DODSON 2,399,474

u HYDRAULIC SERVOMOTOR Filed April 22, 1944 2 Sheets-Sheet l HHH April 30, 1946. E. DODSON 2,399,474

HYDRAULIC SERVOMOTOR Filed April 22, 1944 2 Sheets-Sheet 2 fig. 2.

Patented Apr. 30, 1946 UNITED STATES PATENT OFFICE HYDRAULIC SERVOMOTOB Edward Dodson, Puriton, near Bridgwater, England Claims.

The object of this invention is to provide a hydraulic servomotor which can operate with fluid at very high pressures, i. e. pressures of about 1000 lbs. per sq. in. or more. The use of such high pressures is of great advantage for servomotors to be used on aircraft,e. g., as Jacks for operating the flying controls, because of the resulting saving in weight and size of the jack and conduits.

When high hydraulic pressures are used with a sliding type of valve to control them, a phenomenon occurs which is known as hydraulic lock." While a balanced valve may be perfectly free when exposed to these high pressures and kept moving, if it is allowed to remain stationary for a short period it requires a great efiort to move it again. It appears as if the valve does not remain central in the surrounding sleeve, and that when it gets to one side the whole of the pressure is exerted in forcing it against that side; and curiously when the pressure is relieved it takes an appreciable time before the valve becomes free again.

The invention accordingly provides a high pressure hydraulic servomotor, having a sliding control valve, and comprising a hydraulic relay operating under a much lower hydraulic pressure, e. g. less than 300 lbs. per sq. in., the relay comprising a piston operatively connected to the control valve aforesaid, and a pilot valve for controlling the movement of the relay piston. In this way the application of quite a small force to the pilot valve will be effective to give accurate movement of the sliding control valve of the high pressure servo.

A servomotor of this kind is particularly, but not exclusively, suitable for use as a receiver unit of a fluid-pressure operated remote control system of the kind described in British Patent No. 483,049. The comparatively small changes in pressure in the signal line connecting the receiver unit with the remote sender unit will then be communicated to the pilot valve which, in turn, will transmit a corresponding movement to the relay piston. This, operating under a fluid pressure of 300 lbs. per sq; in. or less, will readily be able to overcome any tendency of the high pressure control valve to stick.

The servomotor preferably includes a device for centralising the main servo piston if the high pressure fails, similar in principle to but different in detail from that described in my United States Patent No. 2,376,671 and also means operating, in the event of failure oi fluid pressure in the signal line, to move the main servo piston to a predetermined position on the same principle as the biassing piston described in my United States Patent No. 2,346,418.

One specific embodiment of the invention will now be described in greater detail, by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a diagrammatic showing of a hydraulic remote control system for operating an aircraft flying control,

Fig. 2 is a vertical section through the receiver unit,

Fig. 3 is a section on the line III-III in Fig. 2, and

Fig. 4 is a section on the line IV--IV in Fig. 2.

The hydraulic remote control system shown in Fig. 1, comprises a. reservoir ill to contain 011, a pump ll serving to feed oil via a pipe l2 to a sender unit l3, a duplicated signal line H leading from the sender unit (which is in the cockpit and actuated by a pilots lever l5) to a receiver unit l8, pipes ll and I8 leading respectively from the receiver unit to opposite ends of a hydraulic jack l9, and pipes 20, 2| serving respectively for return of the oil from the sender and receiver units to the tank. The construction of the sender unit is fully described in my copending United States Patent No. 2,379,692. It operates to set up in the signal line H a hydraulic'pressure which depends upon the setting of the pilot's lever l5, and, in the specific instance under consideration, varies from -200 lbs/sq. in. according to the position of the pilots lever. In the figures the parts are shown in the positions they occupy with the minimum operating pressure of 65 pounds per square inch in the signal line I l. The receiver unit responds, as described below, to variations in the hydraulic pressure in the signal line H' and effects corresponding variations in the position of the servo piston 22 of the jack l9, and therefore of an aircraft control surface 25 operated thereby through the agency of a lever 24. At each end of the duplicated pipe line H is a cut-out valve 23 of the kind described in- British Patent No. 482,935, the cut-out valve 23 associated with the sender unit being located in the body thereof as described in United States Patent No. 2,379,692. The cut-out valves 23 serve, in the event of damage to or leakage from one of the duplicated pipes Hi, to seal off the damaged or leaking pipe while allowing of continued communication between the sender and receiver units via the other pipe.

The receiver unit I6 is, as above explained, used in conjunction with a hydraulic jack I9 of normal type, which contains the high pressure servo piston 22, i. e. the jack provides the necessary power and the receiver unit controls the position of the jack piston. The power supply for the complete installation is all hydraulic, and the receiver unit includes a. preliminary relay 26 operating at about 100 lbs. per sq. in. servo pressure and responding to changes in hydraulic pressure in the signal line I4 produced by the sender unit I3. The jack I9 operates, in the specific example under consideration, at 1000 lbs. per sq. in. pressure.

The signal line pressure is applied through an inlet 21 (Fig. 2) to the lower end of a sensitive piston 28 which operates in a cylinder 28 and is balanced at the upper end by springs 30. The springs 30 bear at their upper ends against a stop 3|, the position of which can be adjusted by means of an adjusting screw 32, and at their lower ends against a'plate 33 carrying a knife edge 34 engaging one side of a double V block 35 on a first swinging link 36. This, as will be seen from Fig. 4, is of bifurcated form and pivoted at the end remote from the knife edge, on pins I36 mounted in the casting I31. The other side of the block 35 is engaged by a knife edge 31 fixed to the piston rod 38. To the piston rod is pivoted at 38 a second swinging link 48, which is loaded by a spring 49 and pivoted centrally at 4| to the pilot valve 42 of the preliminary relay 26 and at its remote end 43 to the piston rod 44 of the relay piston 45.

The pilot valve 42 moves in a sleeve 46 formed with two annular ports, the upper of which 41 is normally subject to reduced pressure at 100 lbs. per sq. in. from a pressure reducing valve 48 (Fig. 3) which will be later described, and the lower of which 58 is normally connected to exhaust (also as later described). The pilot valve has a waisted portion which is in permanent communication with a conduit 52 leading to the upper end of the cylinder 53 containing the relay piston 45. This piston 45 is urged upwardly by a spring 54 operating on the lower end of the sliding control valve 55 of the jack I9 so that the pressure in the conduit 52, which is of the order of 28 lbs. per sq. in., automatically balances that of the spring 54.

If the signal line pressure increases, the sensitive piston 28 moves up and lifts the pilot valve 42. This connects the upper annular port 41 to the conduit 52 and so increases the pressure on the upper end of the relay piston 45, which moves down until the swinging link 48 restores the pilot valve 42 to its neutral position, the increased pressure in the conduit 52 being balanced by the increased compression of the spring 54. Conversely, if the signal line pressure falls, the pilot valve 42 will move down, so connecting the conduit 52 to exhaust via the lower annular port 58 -and allowing the relay piston 45 to rise until the pilot valve 42 is again returned to neutral by the swinging link 48.

The lower end of the piston rod 44 of the relay piston is pivoted at 56 to one end of a third swinging link 51. This has a central slot 58 engaging a pin 58 on a rod 60 connected to the sliding control valve 55. The remote end of the swinging link 51 carries a roller 6| engaging a cam 62 fixed to a lever 63. This is pivoted at its upper end I63, and connected at its lower end by a link 64 (Fig. l) to the lever 24 operated by the jack piston. The sliding control valve 55 is located in a sleeve 65, having upper and lower ports 66, 61 communicating with the return line 2| to the tank. The abutment I68, attached to the lower end of valve 55, for the upper hd of spring 54 has an annular recess I6I to accommodate the lower end I65 of sleeve 65, and so permit of movement of the valve 55 in relation to said sleeve. The sleeve 65 has a central port 69 communicating with a high pressure pipe line 68 leading from the pump II (Fig. 1), and two intermediate ports 18, 1| which are normally masked by the lands on the valve and communicate respectively with the lines I1, I8, leading to the jack. Up or down movement of the relay piston 45 produces through the agency of the swinging link 51, corresponding movement of the sliding control valve 55, which admits high pressure fluid to the jack cylinder to move the jack piston accordingly, the cam 62 acting as a follow up gear to return the sliding control valve to the neutral position. Upward movement of the control valve 55 will connect line I8 to exhaust and line I1 to pressure, so that the jack piston 22 will move to the left as seen in Fig. 1, to an extent determined by the upward movement of the relay piston 45, while downward movement of the control valve 55 will reverse the connections and produce a corresponding movement of the jack piston 22 to the right. The pin and slot connection between the swinging link 51 and the rod 60 provides an adjustment for varying the effective rate of the springs 30 balancing the piston 28 responsive to signal line pressure.

A transfer valve 12 is provided, which acts as a safety device to ensure that in the event of failure of the pump pressure the jack cannot become locked in any position. The transfer valve is a two-position valve controlled by a piston 13 loaded by a spring 14. The transfer valve 12 moves in a sleeve 15 having ports 11, 16 communicating respectively with the lines I1, I8 leading to the jack cylinder. The upper surface of the piston 13 is subjected to the main pump pressure in the line 68 which at any value greater than about 100 lbs. per sq. inch is sufllcient to compress the spring 14. The valve then occupies the position illustrated, in which it closes the communication between the ports 11, 18 so isolating the two sides of the jack. In the event of pump pressure failure the spring 14 moves the valve up, into a position in which its waisted portlon 16 establishes communication between the ports 11, 18, thus coupling the two ends of the jack together. Where, as in the case shown in the drawings, the member to be operated by the jack is an aircraft control surface 25, this is then free to trail in the slipstream. Alternatively, the transfer valve permits manual operation of the controlled member in the event of pump pressure failure.

The reducin valve 48, as explained above, cuts down the pump pressure to 100 lbs. per sq. in. at which pressure the pilot valve 42 of the preliminary relay will operate freely and without friction. It consists of a combined piston and valve balanced by a spring 80. The valve 48 is slidably mounted in a sleeve 8|, in which is an upper annular port 82 communicating by an inlet I83 and a pipe 83 (Fig. 1) with the high pressure line 68, a central port 88 communicating. as later described, with the upper annular port 41 of the pilot valve 42, and a lower annular port 84, communicating via a passage 85 and an outlet I86 with a pipe 86 (Fig. 1) leading to the tank Ill. The port 84 also communicates. as later described.

Until thus decreasing the reduced pressure.

aaeaeve I with the lower annular port 50 of the pilot valve 42. A passage I88 connect the interior of the casting l3! to the port 84, and'thus to the pipe 88. The upper end of the sensitive piston 28 is thus subjected to the exhaust back pressure of the preliminary relay. The same exhaust back pressure acts on the piston valve of the sender unit l3, as described in my U. S. Patent No. 2,379,692. It will be noted that a separate exhaust pipe 2| is provided for the high pressure jack, so that the sensitive piston 28 will not be subjected to the high exhaust back pressure which, under some conditions, may be developed by the jack. As explained inU. S. Patent No. 2,379,692 the signal linepressure is increased, by

the amount of the exhaust back pressure, above that determined by the setting of the pilots lever. As, however, the exhaust back pressure is also operative on the upper end of the sensitive piston of the receiver unit, variations thereof do not aflect the position of said sensitive piston which, in normal operation, moves only in relspouse to changes in the position of the pilots ever.

The port 88 communicates by passages 81, 89 with the space 90 above the reducing valve. This space is normally filled with oil at a reduced pressure of 100 lbs. per sq. in. If the pressure in the space 90 falls below this value, the spring 80 raise the reducing valve, so opening the pressure port 82 and raising the reduced pressure in the space 98. If the reduced pressure in this space rises above 100 lbs. per sq. in., the reducing valve 48 moves down, opening the exhaust port 84 and The reduced pressure is fed to the pilot valve 42 by reason of the communication between the port 88 and the pilot valve, which will now be described.

Between the reducing valve 48 and the pilot valve 42 is an emergency return device which ensures that in the event of failure of the signo.1 pressure the lack will move to a predetermined position. The reduced pressure from the port 88 of the reducing valve is fed to the pilot valve via an intermediate valve 9| loaded by a spring 92. The intermediate valve BI is contained in a sleeve 93, having upper and lower annular ports 94, 95 both of which are connected by a conduit 98 to the reduced pressure port 88, a central annular port 91 communicating by a conduit 500 with the exhaust port 84 oi the reducing valve, and intermediate ports 98, 99 which communicate respectively with the ports 41, 58 of the pilot valve. The valve BI is normally maintained by its spring 92 in the position illustrated, in which it connects the upper annular port ll of the pilot valve to reduced pressure by way of the open port 94 and the lower annular port 5!! of the pilot valve to exhaust by way of the lower waisted portion llll of the valve 9! and port 87. In this position the port 95is closed by the lower land of the valve 9|. The first swinging link 36 carries a roller I02 located above the upper end of the intermediate valve 9!. The pivotal movement imparted-to the swinging link 38 by response of the sensitive piston to changes in signal line pressure is normally insufilcient to afiect the valve 9|, the roller Hi2 only just contacting the valve (as shown in Fig. 3) when the signal line pressure is a minimum and the sensitive piston is at the lower limit of its normal travel. When however, from some abnormal cause, the signal line pressure fails altogether or ward movement of the sensitive piston 28 under the action of the springs to will cause the roller i132 to depress the intermediate valve 9! and so reverse the connections to the ports of the pilot valve 42. This is effected by the upper land of the valve dlclosing the port 94, its lower land opening the port 95, and its central land establishing communication between the port 91 and the upper waisted portion I83 of the valve instead of its lower waisted portion NH. The upper annular port 47 of the pilot valve now communicates with exhaust, via the upper waisted portion )3 of the valve and the port 91, while reduced pressure is fed to the lower annular port- 50 of the pilot valve via port 95 and the lower waisted Portion I (ll of the valve. Under these conditions, the pilot valve 42 will be depressed below its normal position by the swinging lever 40, and reduced pressure from the lower annular port 50 will accordingly be admitted via conduit 52 to the upper end of the relay piston 45. The consequent downward movement of the relay piston will, by rotation of the swinging link 4|! about its connection 39 to the piston rod 38 of the sensitive piston, depres the pilot valve 42 still further until it comes into contact with an adjustable stop Hi4. At this point the pilot valve 42 cannot move any further, and the swinging link 40 will then pivot about its central connection 4| to the pilot valve, so raising the signal line piston 28 against its springs 30. removing the pressure of the roller I82 on the intermediate valve 8!, permits the latter to be raised by its spring 82, until the connections to the pilot valve ports are on the point of being reversed once more. At this point the pressure on the relay piston 35 is relieved and no further movement takes place. The extent of movement of the relay piston, and therefore of the jack, under these emergency conditions is thus determined by the setting of the adjustable stop N14. The setting of this is varied, as desired, by screwing it into or out of the casing of the receiver unit.

By suitably shaping the cam 62, the amount of movement of the jack piston 22, per unit movement of the pilots lever i5, may be made to vary with the angular position of the pilot's lever. Thus in the case of a flying control it may be arranged that over the central range of the lever travel, which will b mainly used in prac-- tical operation, a relatively large amount oi movement of the lever l5 will result in only a small movement of the flying control 25, while towards the ends of the range of travel of the lever, where such delicate control is not required, a large movement of th flying control 25 corresponds to a small movement of the lever.

What I claim as my invention and desire to secure by Letters Patent is:

1. A high pressure hydraulic servomotor, adapted to be remotely controlled by variations in fluid pressure transmitted along a signal line from a distant sender unit, and comprising a main servo piston, a slidingcontrol valve for supplying high pressure hydraulic fluid'to said servo piston to effect movement thereof in either direction, a follow-up linkage connecting said main servo piston and said control valve, a preliminary low pressure hydraulic relay for operating said control valve in response to variations in pressure in the signal line, said preliminary relay including a piston coupled to said control valve, a pilot valve for supplying low pressure hydraulic fluid to and controlling the movement v This, by

of the relay piston and a pressure sensitive device responsive to the signal line pressure and operatively connected to said pilot valve, a pistontype pressure reducing valve for supplying to the pilot valve reduced pressure derived from the high pressure supply, a spring operating on one end of the reducing valve to balance the same against said reduced pressure operating on its other end, said servomotor having pressure and exhaust ports controlled by the pilot valve and connected respectively to reduced pressure and to exhaust by the reducing valve, an intermediat valve between the reducing valve and the pilot valve, means controlled by the pressure sensitive device and operative on failure of the signal line pressure to displace the intermediate valve into position to reverse the connections from pressure and exhaust to the ports of the pilot valve, and a stop for limiting the resulting travel of the pilot valve.

2. A high pressure hydraulic servomotor,

adapted to be remotely controlled by variations in fluid pressure transmitted along a signal line, and comprising a main servo piston, a sliding control valve for supplying high pressure fluid to said servo piston to effect movement thereof, a preliminary low pressure relay foroperating said control valve in response to variations in pressure in the signal line, said preliminary relay including a piston coupled to said control valve, a pilot valve for controlling the movement '01 the relay piston, a sensitive piston exposed to the pressur in the signal line, a balancing spring for balancing the sensitive piston against said pressure, a follow-up link connected at its opposite ends to the sensitive piston and to the relay piston and centrally to the pilot valve, 9. pressure-reducing valve controlling connections from pressure and exhaust to the pilot valve, means controlled by the sensitive piston and operative, on failure of the signal line pressure, to reverse the pressure and exhaust connections to the pilot valve, and an adjustable stop for limiting the resulting travel of the pilot valve.

3. A servomotor as claimed in claim 2, in which the reversing means comprises an intermediate valve located between the reducing valve and the piston valve, a loading spring operating on the intermediate valve, and a pivoted link connected to the sensitive piston, said link being normally ineffective on the intermediate valve but operating to displace it to reverse said pressure and exhaust connections on abnormal movement of asaaeve the sensitive piston due to failure of the signal line pressure.

4. A hydraulic servomotor comprising a first cylinder for connection to a pipe line for transmission of a variable actuating pressure to the servomotor, a sensitive piston in said cylinder, a chamber communicating with the end of said cylinder remote from the pipe line, an exhaust connection to said chamber, a spring in said chamber for balancing the sensitive piston against the pipe line pressure, a relay cylinder, a relay piston located in said relay cylinder, said piston being exposed at one end to the exhaust pressure in said chamber, 'a swinging link operatively connected at its opposite ends to the sensitive piston and to the relay piston, a pilot valve connected centrally to said swinging link, pressure and exhaust ports controlled by said pilot valve, a. high pressure inlet, a reducin valve for supplying reduced pressure from said inlet to the pressure port of the pilot valve, a conduit connecting the pilot valve and the end of the relay cylinder remote from the chamber, said pilot valve operating, under the control of the swinging link and by connecting said conduit alternatively to the pressure port or to the exhaust port, to positnn the relay piston according to the position of the sensitive piston, a high pressure servo piston, a high pressure control valve for controlling the movement of said high pressure servo piston by admitting high pressure to one side thereof and connecting the other side thereof to exhaust, said exhaust connection being independent of the exhaust connection to said chamber, a link operatively connected at one end to the relay piston and centrally to the high pressure control valve, a spring acting on said link to balance the conduit pressure acting on the relay piston, and a follow-up mechanism connecting the other end of said link and the high pressure servo piston.

5. A hydraulic servomotor as claimed in claim 4, comprising a reversing valve located between the reducing valve and the pressure and exhaust ports of the pilot valve, 8. spring for normally maintaining the reversing valve in an inoperative position, means associated with the sensitive piston for displacing the valve into reversing position on failure of the pipe line pressure, thereby admitting fluid to the relay piston to move the latter into said chamber, and an adiustable stop for limiting the resultant move ment of the pilot valve by the swinging link.

EDWARD DODSON. 

